Modelling of condensed flexible bodies considering non-linear inertia effects resulting from gross motions

Abstract

Besides various other application fields, flexible multi-body dynamics simulation is used in particular during the development process of internal combustion engines and power units. Problems such as crankshaft and engine dynamics, radial slider bearing dynamics or noise, vibration, and harshness can be investigated using this methodology. Any specific engine component, called body, can be represented by different methods. Besides beam-mass representations and structured modelling, finite element models are commonly used. As these imply a large number of degrees of freedom, they cannot be applied directly to multi-body dynamics ensuring computational performance. Therefore, condensation methods need to be applied which result in a reduced model with equivalent dynamical properties. This is particularly important if detailed, highly non-linear contact dynamic models, for instance the well-known Reynolds equation, are considered.

Typically, condensation methods are applied to structural matrices of bodies which perform only vibration motions without any global motions. This study outlines a floating frame of reference formulation for condensed components, which perform global motions in addition to the vibration motions. For this purpose, non-linear inertia terms of the reduced body, which result from the global motions need to be computed considering the applied reduction strategy. Both the theoretical background of the formulation and some application examples of the method will be discussed.